Abstract: A filter element (1), with a preferably multilayer structure of a filter medium (3), in pleated form has filter pleats (5, 7) of different pleat heights (h1, h2). The filter pleats (7) with a first pleat height (h1) oppose the filter pleats (5) lower second pleat height (h2). The filter element has a throughflow direction for fluid to be cleaned away from a dirty side to a clean side (R). The transitions arranged adjacent to the inner side all conclude along a fictitious circular cylinder (9), which penetrates the filter medium (3) coaxially to its longitudinal axis (LA).

Abstract: The invention relates to a method for adapting a filter medium to predefinable parameters, such as electrostatic charge, flow-rate behaviour, dynamic pressure behaviour or differential pressure behaviour, fraction filtration efficiency and preservation of a constant quantity and quality of fluid additives. Said method is characterised in that at least one of the aforementioned parameters is adapted by the targeted influencing of the surface energy of the filter medium (18).

Abstract: A filter element (1), with a preferably multilayer structure of a fiber medium (3) that has, in pleated form, filter pleats (5, 7) of different pleat heights (h1, h2), with filter pleats (7) with a first pleat height (h1) and with filter pleats (5) with an opposing lower second pleat height (h2), wherein the filter element has a throughflow direction for fluid to be cleaned away from a dirty side to a clean side (R), is characterized in that the transitions arranged adjacent to the clean side (R) or the dirty side (S) all conclude along a fictitious circular cylinder (9), which penetrates the filter medium (3) coaxially to its longitudinal axis (LA).